Move
Total: £57,750
- SDLT (HMRC)
- £31,500
- Estate-agent fee
- £7,800
- Survey
- £1,500
- Legal (sale + purchase)
- £2,500
- Removals
- £2,000
- Chain contingency (1.5%)
- £12,450
Harrow: is it cheaper to extend or move in 2026?
For homeowners in Harrow (London Borough of Harrow). Updated 2026-06-11.
Outer north-west London. Mix of historic centre (Harrow on the Hill, Pinner Village), 1930s suburban semi-detached (Stanmore, Harrow Weald), and postwar housing. Loft conversions and rear extensions dominate; side returns rare on suburban semis.
The borough covers the HA1, HA2, HA3, HA5, HA7, HA8 postcode districts. Terraced homes here trade around £525,000 against the borough-wide £520,000 average.
In short
In Harrow, the average home is valued at £520,000. Moving up by 60% to a £830,000 property triggers approximately £31,500 in Stamp Duty Land Tax (SDLT). By contrast, a 22 m² high-spec rear extension (single storey) here costs around £108,537 all-in. The average home here is around £520,000 (ONS, 2026).
Your numbers
Adjust the inputs to see your scenario. The page updates instantly as you adjust the inputs.
Your result
Moving is £50,787 cheaper than extending
Extend
Rear extension (single storey) — high spec
Total: £108,537
- Build cost (22 m² × £3,300/m²)
- £72,600
- Professional fees (15%)
- £10,890
- Subtotal
- £83,490
- VAT (20%)
- £16,698
- Contingency (10%)
- £8,349
An extension of this type and size could add roughly £67,600 (≈13%) to your home's value — Nationwide Building Society, October 2025.
Your tipping line
Where moving starts costing more than the extension you selected. The chart follows your inputs above.
Up to about £1,315,000 of target price, moving is the cheaper route in Harrow; beyond that line, extending wins.
Extending in Harrow: what's different here
Local planning picture
- Conservation areas
- 30
- Householder decisions within 8 weeks
- 75%
- Build-cost tier
- outer London
- Typical housing stock
- 1930s semi-detached homes
Decision speed: MHCLG householder statistics, year ending September 2025, excluding agreed extensions of time.
Worth knowing in Harrow
- The average home here is around £520,000 (ONS, 2026).
- Extension types suited to 1930s semi-detached homes: Rear extension (single storey), Rear extension (double storey), Two-storey side extension, Garage conversion, Loft conversion (hip-to-gable), Over-garage extension.
How the £31,500 stamp duty stacks up
HMRC bands applied to a £830,000 purchase — the default Harrow trade-up.
| Price band | Rate | SDLT due |
|---|---|---|
| £0 – £125,000 | 0% | £0 |
| £125,000 – £250,000 | 2% | £2,500 |
| £250,000 – £925,000 | 5% | £29,000 |
What each suitable type costs vs the £57,750 move
High specification at typical size, outer London rates, all-in.
| Extension type | All-in cost | vs moving |
|---|---|---|
| Rear extension (single storey) (22 m²) | £108,537 | £50,787 more than moving |
| Rear extension (double storey) (45 m²) | £208,553 | £150,803 more than moving |
| Two-storey side extension (35 m²) | £167,440 | £109,690 more than moving |
| Garage conversion (18 m²) | £43,056 | saves £14,694 vs moving |
| Loft conversion (hip-to-gable) (25 m²) | £67,275 | £9,525 more than moving |
| Over-garage extension (18 m²) | £34,983 | saves £22,767 vs moving |
Why this comparison matters
"Authorities granted 90% of these applications and decided 93% within eight weeks or the agreed time."
Frequently asked questions
- Is it cheaper to extend or move in Harrow?
- At Harrow's average £520,000 home moving up to £830,000, the move costs about £57,750 — including £31,500 of HMRC Stamp Duty. A 22 m² high-spec rear extension (single storey) runs roughly £108,537 at outer London rates. Moving is cheaper here by about £50,787. Your real figure depends on extension size, specification and planning constraints.
- At what price does moving stop making sense in Harrow?
- Starting from Harrow's average £520,000 home with a 22 m² high-spec rear extension (single storey) (£108,537 all-in), the tipping line sits at roughly £1,315,000: buying above that price costs more in SDLT and moving fees than the extension itself. Below it, moving stays the cheaper route. The live chart on this page recalculates the line for your own inputs.
- How much stamp duty would I pay moving up in Harrow?
- On a typical Harrow trade-up from £520,000 to £830,000 (a 60% step up), Stamp Duty Land Tax (SDLT) is £31,500 — an effective rate of 3.80%. First-time buyers and additional-property buyers pay different rates. Use HMRC's official calculator at tax.service.gov.uk for your exact figure. HMRC Stamp Duty calculator
- How much does an extension cost in Harrow in 2026?
- Budget around £109,000 all-in for a high-spec 22 m² rear extension (single storey) here — outer London build rates run near £3,300/m². For a 45 m² rear extension (double storey) expect roughly £209,000. Those totals already carry 15% professional fees, 20% VAT and a 10% contingency; access, specification and ground conditions move the final number.
- How long does planning permission take in Harrow?
- The statutory determination period for a householder application is 8 weeks. London Borough of Harrow decided 75% of householder applications within 8 weeks in the year to September 2025 (MHCLG figures, excluding agreed extensions of time). Across London, authorities grant roughly low-to-mid 80s per cent of applications. A householder application costs £548 from April 2026, and a Larger Home Extension prior approval £240.
- Do I need planning permission for an extension in Harrow?
- Many single-storey rear extensions fall under Permitted Development — no planning permission needed. Harrow has Article 4 directions in conservation areas (notably the Harrow on the Hill Conservation Area) plus borough-wide HMO Article 4. The Harrow on the Hill direction removes PD rights for most external alterations and applies to a small footprint. Harrow has 30 conservation areas, including Harrow on the Hill, Harrow Weald, Pinner Village, where PD rights are curtailed. Side extensions, large rear extensions and most wraparounds need full planning regardless. Check the London Borough of Harrow planning portal first. Open the London Borough of Harrow planning portal
- How long does a rear extension (single storey) take in Harrow?
- Allow around 16 weeks on site for a typical rear extension (single storey) in Harrow, after design, party wall agreements with neighbours and the council's determination period. A rear extension (double storey) runs nearer 20 weeks. End to end, plan 4–8 months from first call to completion — longer in conservation areas or where structural surveys are needed.
- How much value does an extension add in Harrow?
- On a £520,000 Harrow home, the uplift is roughly £67,600 to £124,800: Nationwide Building Society (October 2025) put an extra double bedroom at about 13% of value, and a full loft conversion plus extension at up to 24%. The realised return depends on your street's ceiling price, buyer demand in Harrow and the specification you choose.
- Can I live in my home during the extension build?
- Most Harrow families stay in their home during a rear extension or garage conversion — works are contained to one side of the house. Two-storey side extensions and hip-to-gable lofts are noisier: expect 4–6 weeks where one floor or the driveway side is out of action. Plan temporary kitchen arrangements and dust control for the noisy weeks.
Compare nearby London boroughs
Nearby by average property value — useful if you're weighing a move to an adjacent price tier. A comparable trade-up in Waltham Forest would carry the same £31,500 of stamp duty.
Methodology and sources
Stamp Duty Land Tax is calculated from the HMRC bands in force for the 2025–26 tax year. Verify any figure against HMRC's official calculator before committing. Extension costs use outer London £/m² rates by extension type — industry-estimate midpoints, presented as approximations.
- HMRC SDLT calculator — tax.service.gov.uk/calculate-stamp-duty-land-tax
- GOV.UK Stamp Duty Land Tax guidance — gov.uk/stamp-duty-land-tax
- Nationwide House Price Index (October 2025 release) — value-add commentary attributed to Andrew Harvey, Senior Economist.
- HM Land Registry / ONS UK House Price Index — borough average property values (March 2026 release).
- MHCLG planning statistics (PS2 dashboard) — householder decision speed, year ending September 2025.
- London 2026 £/m² grid by extension type and tier — Build Team benchmark compiled from BCIS/RICS, FMB and published architect guides (refreshed quarterly).
- Conservation-area counts and Article 4 status — individual London borough councils, verified 2026.